CSLB C-20 HVAC ContractorHeating SystemsMedium
A technician is installing a new 92% AFUE condensing furnace. The furnace manufacturer's instructions specify using Schedule 40 PVC for the vent piping. According to California Mechanical Code (CMC) and common practice, what is the maximum recommended unsupported horizontal length for this type of vent pipe between hangers?
- A5 feet (1.5 meters).
- B4 feet (1.2 meters).
- C3 feet (0.9 meters).
- D6 feet (1.8 meters).
Show answer & explanationAnswer & explanation
Correct answer: B. 4 feet (1.2 meters).
For Schedule 40 PVC vent piping, the California Mechanical Code (CMC) and industry best practices generally recommend a maximum unsupported horizontal span of 4 feet between hangers to prevent sagging and maintain proper slope for condensate drainage.
Why the other options are wrong
- A. 5 feet is generally too long for horizontal PVC vent pipe without risk of sagging, which can create traps for condensate.
- C. 3 feet is often used for heavier piping or specific conditions, but 4 feet is standard for PVC.
- D. 6 feet is significantly too long for horizontal PVC vent pipe, making sagging and condensate issues highly probable.
PVC Vent Hanger Spacing
The maximum allowed distance between supports for horizontal PVC vent piping in condensing furnace installations to maintain structural integrity and proper slope for condensate drainage.
- Prevents sagging and water traps.
- Critical for proper condensate removal.
- Typically 4 feet for Schedule 40 PVC.
Memory trick: PVC vent, 4 feet, no sag, no defeat.